1. Technical Field
The field of the invention relates to engine systems using pressure sensors. In particular, the field of the invention relates to systems that use a determination of barometric pressure.
2. Background of the Invention
Engine systems are known which utilize exhaust gas recirculation (EGR) to reduce engine emission and increase fuel economy. In one example, two pressure sensors are utilized not only to calculate EGR flow into the engine, but also to control air-fuel ratio. Typically, one sensor is coupled to the intake manifold and another is coupled in the EGR pathway between an EGR valve and an orifice. Such a system that provides dual use of sensors can offer cost advantages. Such a system is described in U.S. Pat. No. 6,138,504.
The inventors herein have recognized that there is a potential that the pressure sensors in such a system may degrade. In particular, if the intake manifold pressure sensor degrades, engine air-fuel ratio control may degrade thus affecting emissions. Further, if the pressure sensor coupled to the EGR system degrades, EGR flow control and flow estimation may degrade.
In one example, the above advantages over prior approaches are provided by a method for controlling an engine coupled to an exhaust gas recirculation system, the engine coupled to a first pressure sensor and the exhaust gas recirculation system coupled to second pressure sensor. The method comprises determining whether at least one of the first and second pressure sensor has degraded, and in response to said determination, discontinuing exhaust gas recirculation and calculating an engine air intake amount based on the other of said indicated at least one pressure sensor.
By utilizing the remaining operational pressure sensor when one pressure sensor has degraded, it is possible to accurately determine air entering the engine and therefore accurately control engine air-fuel ratio. This is particularly true since EGR has been discontinued. For example, the amount of EGR flowing into the engine affects the amount of fresh air inducted for a given manifold pressure. Thus, by discontinuing EGR, this error source is removed and accurate air determination is possible even with a reduced sensor set.
An advantage of the invention is improved engine control during sensor degradation.
Another advantage of the invention is that engine operation can be continued even when sensor degradation occurs.